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What is the safest preservative in cosmetics and skin care products?

What is the safest, most advanced and least irritating preservative in cosmetics and skin care products? In other words, what kind of preservatives are generally used by high-end brands or brands that advocate plant skin care?
Transfer from Zhihu, Yu Xiao (excellent respondent under the topic of beauty and skin care)

The preservatives in cosmetics are generally safe as long as they are used in accordance with the requirements of laws and regulations. Plant preservatives are not reliable!
Many people frown when they hear “preservatives”, and they think it is not a good thing. So why do you hate preservatives so much? First, this name makes people feel uncomfortable. If the name is changed to antibacterial, it will be easier for everyone to accept. Maybe everyone is still welcome to add such ingredients. The second is that individual media reports on a very small number of problems have caused consumers to lose confidence in these qualified preservatives.

Why should preservatives be added to cosmetics?

That’s because in general, most of the formulations of cosmetics are emulsified systems. What is an emulsification system? In layman’s terms, the “water” and “oil” are kneaded together through the peacemaker “emulsifier” to form a milky texture. The advantage of this is that the resulting cosmetics have a more advanced texture and a skin feel. It is not oily and not greasy, and it has better moisturizing properties.
But in this way, we must face the problem of microorganisms, because cosmetics contain both “water” and “oil”. These are the necessary conditions for the survival of microorganisms. Therefore, the characteristics of the cosmetics formula determine that it is a microorganism. A breeding ground, and cosmetics are generally used for multiple openings, which brings the risk of breeding bacteria, so preservatives must be added to cosmetics. Increase shelf time and use time after opening the lid.
Preservatives are indeed not beneficial to the skin; however, it is absolutely impossible to do without preservatives, and the non-preservatives claimed by cosmetics nowadays are not non-preservatives, but preservatives that are not within the scope of the law are added. In fact, think about it carefully, is it safer to use ingredients that are not restricted by the law? Or is it safer to use ingredients that are strictly required and reviewed by the law?

Conventional preservative categories

1. Formaldehyde and formaldehyde emitters
At the very beginning of the skin care industry, some manufacturers did add formaldehyde to their products to prevent the overgrowth of bacteria. Later, because this practice caused a lot of irritation and dermatitis, chemists began to think of ways to replace the formaldehyde body with something that can release formaldehyde very slowly, so that the bacteria can be inhibited without a large amount of formaldehyde and the human body. get in touch with.
Typical preservatives of this type are DMDM ​​hydantoin, imidazolidinyl urea, and bis(hydroxymethyl) imidazolidinyl urea-in short, the ones with the word “urea” are inseparable.
2. Paraben esters
The association between this type of preservatives and breast cancer has never been confirmed by large-scale experiments. The cases of contact dermatitis caused by these products are the least. In fact, in terms of short-term toxicity, parabens are the safest known preservatives.
There are 4 kinds of parabens, one for methyl ethyl propyl butyl, “butyl paraben”
3. Isothiazolinones
Research on isothiazolinone preservatives has shown that this type of preservative is the most likely to cause contact dermatitis among all preservatives.

Such preservatives are mainly methyl isothiazolinone and methyl chloroisothiazolinone. If you are determined to buy products that contain this kind of preservatives (some of Estee Lauder’s formulas contain them), then I suggest you try a sample first, and don’t get caught.
4. Iodopropynol butyl carbamate
This type of preservative is the only one, which seems to be relatively mild at present, and there are also cases of allergies. The irritation to the mucous membrane is relatively large, and it cannot be used on the lips.

Closer to home, let’s talk about the irritation of several commonly used cosmetic preservatives. Say nothing, just use experiments to prove it.

cosmetic preservative

Preservatives are one of the main causes of skin irritation and contact allergy. At present, there are many kinds of preservatives commonly used, including phenoxyethanol, methyl paraben, propyl paraben, imidazolidinyl urea and DMDM hydantoin. The above article comprehensively evaluated the skin irritation of the above-mentioned commonly used preservatives at the concentration prescribed by law, and provided help for everyone in the selection of preservatives.
Specifically, researchers used patch test and repeated coating test (ROAT) to evaluate skin irritation on humans. In vitro test methods such as keratinocyte toxicity test, red blood cell (RBC) test and egg chorioallantoic membrane (HET-CAM) test were used to study the mechanism of preservative-induced irritation.

cosmetic preservative 2

Figure 1 In the patch test, all preservatives showed slight irritation


The patch test showed that all test substances showed a weak erythema reaction. In the patch test, propylparaben has the highest occlusive irritation due to the damage to the cell membrane. The two formaldehyde releasing agents exhibited cytotoxicity to keratinocytes and showed obvious skin irritation in repeated coating tests.

cosmetic preservative 3

Figure 2 In the repeated patch, the formaldehyde release systems of the two parabens showed the greatest irritation


After using phenoxyethanol and two propyl parabens, obvious irritation can also be observed. In the egg chorioallantoic membrane test, no preservative penetrated into the blood vessels, which may be because the current safe dose of preservatives does not change the subcutaneous blood vessels.

Figure 3 Hemolysis experiment


Overall, this study provides experimental evidence: at acceptable concentrations, due to cytotoxicity to keratinocytes and damage to cell membranes, commonly used cosmetic preservatives have mild skin irritation and mild erythema reactions. The use of occlusive agents in patch tests may result in more sensitive skin. Under the commonly used conditions of cosmetics, phenoxyethanol and parabens are mild to the skin, while DMDM and imidazolidinyl urea have obvious skin irritation to keratinocytes. These findings indicate that the combination of in vivo and in vitro tests may provide a comprehensive test pool to evaluate and compare the skin safety of individual cosmetic ingredients and understand the underlying mechanisms.

Yu Xiao

Yu Xiao

Transfer from Zhihu

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